German Patent 2,550,165 discloses an intake arrangement for combustion air which drives a portable hand-guided work apparatus, namely, an air cushioned lawnmower. The intake arrangement comprises a cylindrical housing wherein an intake airflow is tangentially guided. The cylindrical housing serves as a centrifugal-force separator for separating and discharging contaminants in the inducted air. The air filter is connected to the center of the centrifugal-force separator wherein the precleaned air is guided. The air filter comprises a thick-walled fine filter which requires an application of oil in order to filter out fine dust. The intake arrangement requires continuous control and maintenance, especially when the intake air is heavily laden with dust.
It is an object of the invention to provide an intake arrangement for the combustion air of an internal combustion engine of a portable handheld work apparatus which has a high service time with low maintenance.
The intake arrangement of the invention is for combustion air of an internal combustion engine including an internal combustion engine of a portable handheld work apparatus wherein the combustion air drawn toward said engine is laden with dust. The intake arrangement includes: an air filter mounted upstream of the engine for separating the dust from the combustion air; a centrifugal-force separator for receiving a flow of combustion air and for dividing the flow into a central core flow having essentially fine particles of the dust and a tangential flow surrounding the central core flow; the air filter being connected to the centrifugal-force separator so as to cause the central core flow to flow to the air filter; and, supply means for supplying a carrier airflow containing coarse particles of the dust to the air filter to permit the coarse particles to build up a filter cake on the air filter to separate out the fine particles in the central core flow.
The low-dust core flow of the centrifugal-force separator conducts essentially the finest particles. In addition to the core flow, the air filter is charged with an additional carrier airflow which conducts coarse particles in coarsely pregiven quantities. The particles have a mean grain diameter which is suitable to build up a filter cake on the air filter. The filter cake functions to separate the finest particles in the core flow of the centrifugal-force separator which is directed to the air filter. The additional carrier airflow is practically formed by the tangential flow of a further centrifugal-force separator. The core flow is understood to be the gas flow or airflow which flows axially about the longitudinal center axis of a centrifugal-force separator; whereas, the tangential flow moves radially outside of the core flow and tangentially and axially along the inner wall surface of the casing or housing of the centrifugal-force separator. Because of the centrifugal forces, larger particle fractions are present in the tangential flow than in the core flow wherein only the finest particles having low mass and small diameter are present.
In this way, an intake arrangement for the combustion air of an internal combustion engine is provided which operates in accordance with the cake-filtration principle notwithstanding a centrifugal-force separation upstream of the air filter. The maintenance intervals of the air filter are significantly extended in this way. The intake arrangement saves space and can be configured of an air filter and one or several centrifugal-force separators for use in portable handheld work apparatus. Preferably, cylindrically-shaped axial cyclones having an axial air feed are used as centrifugal-force separators. It can also be practical to configure the centrifugal-force separators as cyclones having a cylindrical housing section and thereafter a conically tapering housing or even as a turbofilter.
A spin flow is present during operation in the centrifugal-force separator. The spin flow can be effected in that the particular intake opening of the centrifugal-force separator is arranged tangentially on the housing thereof while the clean air exit is arranged axially on the housing. A spin flow can also be effected by corresponding gas or air conducting elements at the air entry or in the interior of the centrifugal-force separator.
The carrier airflow, which is additionally applied to the air filter and mostly has coarse particles, is advantageously picked up via a suitably shaped dip pipe which the tangential flow surrounds in the interior of the second centrifugal-force separator. It can be practical to take off the additional carrier airflow with a dust channel opening tangentially at the second centrifugal-force separator. In this way, mostly coarse particles having a larger grain diameter are supplied to the air filter. The air filter is mounted downstream of the centrifugal-force separators and is connected in series therewith. In this way, a filter cake can be built up on the air filter after the engine of the work apparatus is started and this filter cake separates even the finest particles from the combustion air. In this way, a permanent, minimum service operation of the engine is provided and the effectively purified combustion air is substantially free of abrasive fine dust when entering the engine.
A compact intake arrangement comprises two first centrifugal-force separators and a second centrifugal-force separator as well as an air filter. The centrifugal-force separators are fluidly connected to each other so that the core flows of the first centrifugal-force separators and the tangential flow of the second centrifugal-force separator are supplied to the air filter.
A blower is used to generate an airflow through the centrifugal-force separators. The blower can be the cooling fan of the engine. In this way, the intake work of the engine can also be reduced. The air filter is connected to the dip pipes of the first centrifugal-force separators and to the dust channel of the second centrifugal-force separator. To discharge the dirt particles from the intake arrangement, a fluid connection of the tangential flows of the first centrifugal-force separators and the core flow of the second centrifugal-force separator to the inlet of the blower is provided. The air filter can be configured as a simple membrane filter, preferably as a flat paper membrane.